The inversion in US Treasurys is not as previous inversions. Prior to 2014, the Fed following Fisherian principles applied to contemporaneous factors would tighten and the longer maturities stay close to long term expected NGDP expected growth. The shorter maturities....

...was anticipated to be a cyclical temporary slowing if the economy. Now the longer maturities are staying sticky with rates below shorter maturities as they anticipate a return to chronically low rates and resulting capping of king term growth. In many ways this inversions...

...reflects the opposite expectations of the previous inversions.
If the market is convinced that the Fed will complete normalization, long maturities will rise to the anticipated higher schedule of long term NGDP, unfettered by the Fed faux Wicksell. Then, after possibly 6%

....ten year US Treasurys, reflecting a 5% to 7% long term NGDP annual growth, the Fed might go to a Taylor Rule. Then the inversion will signal a possible monetary policy induced economic slowdown - but temporary.

By then SP500 should reach 6000 or so before they trade down as per a monetary policy induced business slowdown.
Not now.